Debugging your code can be tricky, and that Serial.print() comes in very handy. Unfortunately, you can't always connect your robot to your PC, because the cable is heavy and limited in length. A bluetooth or wifi module may help, but setting it all up is a pain. And adding a display to your robot makes the code that you were supposed to debug even more complex, not to mention the resources it takes.
To solve that, I made this simple serial terminal. It's just a Nokia display and an Arduino Pro Mini, all soldered together to form a compact little device. You connect it to your robot's serial, and can immediately see what is happening in its brains.
While this project pretty much works and serves its purpose, it's not the most ergonomic design on earth. So I decided to make an even smaller version, this time with a more thought out user interface. I called it #Nano TTY, because it's even smaller than the Micro TTY here. It uses pretty much the same idea, but has an OLED screen for display and a rotary encoder for scrolling.